Treatment of zinciferous materials containing lead and/or cadmium



L. E. TETER Oct. 28, 1930.

TREATMENT OF ZINCIFEROUS MATERIALS CONTAINING LEAD AND/OR CADMIUM Filed Sept. 22, 1928 INVENTOR ATTORNEYS Patentea D nis, 1930 T T TE [PAT NT oFFIcE LLOYD or PALMERTON, r'nNNsYLvANIA, ASSIGNOB TO THE NEW JERSEY "ZINO COMPANY,1OF NEW YORJ,I, 'N. Y., A CORPORATION OF NEW JERSEY TREATMENT OF zINcmERoUs MATEBTALS coNrAmING LEAD AND/OR camunm Application fi1ed September:

This invention relates tothe treatment-oi:

zinciferous materials Containing lead and/rcadmium and perhaps other contaminating metals. The invention aims to provide an improved method of'etfecting a substantial removal orelimi-nation of lead and/or'cadmium and other contaminating metals from such zinciferousmaterials. p

Lead and cadmium: are'common contaminants of zinc ores' and their concentrates. In addition, cert ain metals'such as tin, antimo bismuth, etc., are commonly present inizii? ores. Appreciable amounts of these contain nating metals find thei'r'way into the product of the zinc recovery operation and thereby con'tam'inatethe zinc product obtained therefrom. Lead and cadmium are technically the most commonly recognized contaminants of zinc ores and their concentrates, and when present in relatively small amountsieconomicallyprevent theproduction-of highgrade Z1110 produc,t's,"such as zinc metal, zincoxide,

zinc dust, et c.,substantially free of-lead and "cadmium. A relatively large tonnage of zinc concentrates containing up to 5 of lead-andsubstantial percentagesflof cadmium are available for, zincsmelt'ing, "but it appears that no entirely satisfactory pyrometallurgical method 'has heretofore been proposedfor effecting a substantial removalor elimination of lead"and/or cadmium" from suoh'zinc con-. centrates." i

The object of the present invention is to provide a pyrometallurgical treatment for zinciferousmaterials containing lead, cadmium orother contaminating metal in the course of which a substantial removal of the contaminating metalso is efiected, thereby making possible the recoveryof a purer and more desirable zinc. product from the zin-clfer;

- one material than couldotherwise be ohtaind. Since, in the practice of the inve'ntion all of the contaminating metals appear to behave similarly, I will herein more particularly describe 't-heinyention with respect a2, 1928. Serial No. 307,739,,

to the elimination of lead and-cadmium.- The invention may be practiced primarily for the elimination of lead without special regard to the elimination of otlier metals, or it'may be practiced for-the elimination of any' one or more of the contaminating metals. In general, the elimination of substantially all of the lead from the zinciferous material by the practice of the inventionwill at the same time effect a substantial elimination of such others of the contaminating metals as may be present. V g

The present invention is based on my discovery'that inblast roasting a 'ch'arge of zinciferous material a substantialsegregation or concentration of lead and cadmium takes glace in any relatively cool area of the charge. ased on this discovery, my present invention involves subjecting the zinciferous material in the presence of a suitable combustible agent ,to a blast-roa'sting.treatment in thecourse of v which a substantial amount of lead and/or cadmium segregates in a relatively cool area of the material, and then. mechanically separating strch area'or portion in which lead and/or cadmium has so segregated from the remainder of the material, tilization of lead and cadmium is very materially' promoted by the presence of a chlo ridizin'g agent, if such achloridizing agent be added the concentration or segregation of lead and cadmium in the relatively coolareas of the charge' will be materiallyincreased.

present invention isfparticularly ap- "plicable to thefltreatment of flotation concen- I trates. On account of their fine state of subdivision, such concentrates are difficult to handle, moreparticularly'in the smeltingoperation. Inacco rdance with the present invention, these concentrates a're first sub jected to an ordinary desulfurizing or roast-- ing treatment, in the course of which the sul-' ,fur content ispreferably reduced to around 23 The roasted concentrate is then mixed with a small amount of carbonaceous fuel, such as coke, coal, or the like, and then removed from the 'zinciferous material by cooler layer at the gas-exiting surface.

volatilization and condenses in part near the The portion in which the lead and cadmium have segregated is then separated from the remainder of the resulting sintered material in any appropriate way.

Chloridizing agents of any kind added to or brought in contact with the zinciferous material react with the lead and cadmium present therein to. form volatile chlorides. These chlorides, and thus the lead and cadmium, are removed in part from the zinciferous material by volatilization, and condense in part near the blast-exiting surface of the charge:

The practice of the present invention in its complete and preferred aspect provides a combination of the following features 1. A preliminary roasting operation followed by a roasting'treatment-with a small amount of carbonaceous material on a sintering machine.

- 2. Chloridizing sintering, that is, the combination of a sintering blast roast with a chloridizing roast.

3. Fractional volatilization of lead chloride and cadmium chloride.

4. Completion of the removal of the lead v and cadmium by (a) shaving 011' the bottom portion of the charge into which lead and cadmium have concentrated and by (b) screening out the pulverulent cadmium-bearing material on the top of the sintered char e.

As a result of this treatment the finely ivided ore is sintered, thus agglomerating it and rendering it easier to handle than the original roasted concentrate.

Furthermore, desulfurization' is completed, the remnant of sulfur in the roasted concentrate (2 to 3%) is substantially removed'or reduced to less than 0.5%by the blast-roasting treatment. And finally a very effective removal of lead and cadmium is accomplished, thereby'permittingthe production of purer and more desirable zinc products from the zinciferous material; I p I Any zincexpelled as oxide from thezinciferous material during the blast-roasting treatment, together with the volatilized lead and cadmium, may be-recovered in the form of fume by passing the waste gases from the sintering machine through any appro .priate form of fume collector, such,'for example, as a bag-house.

The preliminary roasting of the zinc ore may be carried out in any appropriate roasting apparatus. I prefer to conduct this roasting operation soas to leave not more than from to 3% of sulfur in the roasted product. If desired, however, a larger percentage of sulfur may be left in the product of this preliminary roasting operation and may be utilized as the combustible agent or fuel in the subsequent blast-roasting treattaining lead and cadmium, such as a roasted flotation concentrate, is mixed with 4 to 12% of coal and 2 to 5% of sodium chloride or calcium chloride or other chloridizing agent. The mixture is then charged into a sintering machine of the blast roasting type, such, for example, as the well-known Dwight- Lloyd sintering machine. The pallets ofthe sintering machine are, as is usual, protected by a hearth layer or grate dressing of previously treated charge. This hearth layer is advantageously prepared of sinter or inert material through inch screen and on inch screen. The charge of the sintering machine is ignited by an oil burner or other appropriate means and then sintered and roasted by an 'air blast drawn through the charge. In the Dwight-Lloyd sintering machine, this air blast is drawn downwardly through the charge on the pallets. Thus, with the Dwight-Lloyd sintering machine, a.very substantial segregation or concentration of lead and cadmium occurs in the bottom inch or half-inch of the charge and hearth layer.

The surface portion in which lead and cadmium have concentrated is then removed from the remainder of the resulting sintered charge. Thus, with the Dwight-Lloyd sintering machine substantial removal of lead and cadmium can beefi'ected by separating the bottom inch or'half inch of the sintered charge from the overlaying portion. Thisseparation may be effected in any appropriate manner.

The single figure of the accompanying drawing diagrammatically represents. a blast roasting or sintering machine of the Dwight- Lloyd type equipped with a sinter separating means for practicing the present invention. The sintering machine comprises an endless series of traveling pallets 5 provided with perforated grates or hearths 6. A feed hopper 7 is provided for charging the zinciferous material into the allets and an oil burner hood 8 is. provided or igniting the charge. Air is drawn downwardly through the charge into a wind-box 9 and to an outlet 10 by a fan (not shown).

The pallets 5 move in the direction of the arrow. A horizontal knife 11 is appropriately supported near the discharge end of the sintering machine. This knife is positioned at such a level as to shave off the bottom inch or half-inch of the charge and the. hearth layer. The sintered charge is forced against this knife by the motion of the pallets and is held down against the grate by a roller 12 appropriately mounted above the charge and provided with flanges 13v to force the charge against the knife. The roller is driven by a sprocket wheel and chain 14 at a slightly greater peripheral speed than the speed of the pallets.

It has been found advantageous to equip the knife 11 with saw teeth 11, which may be beveled alternately up and down. It is also advantageous to produce a reciprocal motion of the knife, either back and forth parallel to the motion of the charge, in which case the knife acts as a chisel, or to and fro at right angles tothe motion of the charge, in which case the knife acts as a saw.

The portion of the sintered charge above the knife 11 is advanced into a chute 15 and appropriately collected. That portion of the fbund at the top surface of the sintered charge, partly in the form of a soft pulverulent sublimate containing cadmium, lead and zinc, and partly in the soft top of the sinter, which has been only partly sintered on ace count of the rapid cooling to which it has been subjected by the blast of the sintering machine. This lead and cadmium-rich top surface is discharged with the bulk of the sintered material into the chute 15, and, where the sinter is sufficiently hard, may be screened out with the fines from the remaining sinter, thus further decreasing the lead and cadmium content of the latter. This top portion may also advantageously be subjected to a repeated or multiple sintering action.

The following examples illustrate the advantageous results secured by the practice of the invention on zinc concentrates made by differential flotation. The zinc concentrate .Sixth A-inch section;

was first roasted in accordance with customary practice.

In one case, the roasted concentrate was mixed with an appropriate amount of carbonaceous fuel and slntered on a Dwight- Lloyd machine. The distribution of the lead and cadmium in the vertical cross section of the resulting sinter was'as follows:

' Per cent Top 34-inch section 0. 012 Second 34-inch section 0. 014 Third )-inch section... 0. 007 Fourth 54-inch section. 7 Fifth A-inch section..

Seventh 54-inch section "I: Eighth (bottom) %-inch section knife would contain about 8.6% lead and about 0.25% cadmium.

In another case, a roasted zinc concentrate was mixed with 2 of sodium chloride, together with the usual amount of carbonaceous fuel for sintering, and treated in accordance with the principle of the present invention. The roasted concentrate analyzed approximately as follows:

is. E. i 65.1 4.3 0.12 2.8

Thetop and bottom portions (divided by the cutting knife) of the sintered product analyzed as follows:

211 Pb Cd c1 s Portion of sinter above kniie 63.6 1. 5 .01 .117 .eo Portion of sinter below knite...- 60. 7 2. 9 05 914 1. 20

Zn Pb Cd C] l S Portion of sinter above knife... 65. 6 .41 003 25 i 46 Portion of sinter below knife... 61. 9 i. 30 .030 1. 13 I 77 In another case, the roasted zinc concentrate was mixed with l calcium chloride, together with carbonaceous fuel for sintering, and treated in accordance with the present invention. The top and bottom portions (divided by the cutting knife) of the sintered product analyzed as follows:

Zn Pb Cd Cl S Portion of sinter above knife 63. 7 46 005 120 32 Portion of sinter below knife 62. 0 1. 00 010 560 57 In still another case, the roasted zinc concentrate was first mixed with 2 70 of so dium chloride and carbonaceous fuel and sintered on a Dwight-Lloyd machine without separation of the top and bottom portions of the resulting sinter. This sinter was appropriately crushed and mixed with additional carbonaceous fuel and 2 of sodium chloride and treated in accordance with the principles of the present invention. The top and bottom portions (divided by the cutting knife) of the resulting resintered product analyzed as follows:

Zn Pb Cd Cl S Portion of sinter above knife" 64. 0 26 002 058 14 Portion of siuter below knife. 62. 2 72 .004 .1398 52 The distribution of the lead and cadmium in the vertical cross section of the resintered product was as follows Pt) I Cd Top 95 inch section. Second )6 inch section Third inch section Fourth }4 inch section Fifth )6 inch section.. Sixth 54 inch section Seventh 36 inch section 7 Eighth (bottom) inch section o. 003 i N ot detected I d (l I claim: Y

1. The improvement in the treatment of zinciferous material containin lead and/or cadmium which comprisesisii bjecting said material to a sintering operationby passing a combustion supporting gas through an appropriately supported'layer of-the material and a suitable combustible agent in the course of which operation a substantial amount of' lead and/or cadmium segregates near one surface of said layer, and mechanically sepa i course of which operation a substantial amount of lead and/or cadmium segregates near one surface of said layer, and mechanlcadmium which comprises subjecting said I material to a sintering operation by passing a combustion supporting gas through an appropriately supported layer of the material and a suitable combustible agent in the course of which operation a substantial amount of lead and/ or cadmium segregates near one surface of said layer, mechanically separating such surface portion in which lead and/or cadmium has so segregated from the remainder of the resultingsintered product, and subjecting said remainder of the sintered product to a separative treatment for the removal therefrom of pulverulent material of relatively high lead and/or cadmium content.

4. The improvement in the treatment of zinciferous material containing lead and/or cadmium which comprises subjecting said material to'a sintering operation by passing a combustion supporting gas through an appropriately supported layer of the material and a suitable combustible agent in the presence of a chloridizing agent in the course of which operation a substantial amount of lead and/or cadmium segregates near one surface of said layer, mechanically separating such surface portion in which lead and /or cadmium has so segregated-from the remainder of the resulting sintered proclnot, and subjecting said remainder of the sintered product to a separative treatment for the removal therefrom of pulverulent material of relatively high lead and/or cadmium content. v r

5.-The improvement in the treatment of zinciferous material containing lead and/or cadmium which comprises subjecting the material in the presence of a suitable combustible agent to a blast-roasting treatment in the course of which a substantial amount of lead and/or cadmium segregates near the blast-exiting surface of the material, and separating such surface portion in which lead and/or cadmium has so segregated from the remainder of the material.

6. The improvement in the treatment of zinciferous material containing lead and/0r cadmium which comprises subjecting the material in'the presence of a suitable combustible agent and a chloridizing agent to a blastroasting treatment in the course of which a substantial amount of lead and/or cadmium the material, and separating such surface portion in which lead and/or cadmium has so segregated from the remainder of the material. I

7. The improvement in the treatment of roasted zinc concentrates containing lead segregates near the blast-exiting surface of.

and/or cadmium which comprises subjecting the roasted concentrate to a sintering operation by blast roasting in the course of which a substantial amount of lead and/or cadmium segregates near the blast-exiting surface of the sintered product, and separating such surface portion in which lead and/or cadmium has'so segregated from the remainder of the sintered product.

8. The improvement in the treatment of roasted zinc concentrates containing lead and/or cadmium which comprises subjecting the roasted concentrate to a sintering operation by! blast roasting in the presence of a chloridizing agent in the course of which operation a substantial amount of lead and/or cadmium segregates near the blast-exiting surface of the sintered product, and separating such surface portion in which lead and/or cadmium has so segregated from the remainder of the sintered product. 7

9. The improvement in the treatment of zinciferous material containing lead and/or cadmium which comprises subjecting said material to a sintering operation by passing a combustion supporting gas through an appropriately supported layer of the material and a suitable combustible agent in the course of which operation a substantial amount of lead and/0r cadmium segregates near one surface of said layer, mechanically separating such surface portion in which lead and/or cadmium has so segregated from the remainder of the resulting sintered product, and subjecting said remainder of the sintered product to another similar sintering operation.

10. The improvement'in the treatment of zinciferous material containing lead and/or cadmium which comprises subjecting said material to a sintering operation by passing combustion supporting gas through an appropriately supported la er of the material and a suitable combusti, 1e agent, crushing the resulting sintered material, mixing the crushed sintered material with additional combustible agent, and subjecting said mixture to a sintering operation by passing a combustion supporting gas through an appropriately supported layer of the material in the course of which operation a substantial amount of lead segregates near one surface of said layer, and mechanically separating such surface portion in which lead and/or cadmium has so segregated from the remainder of the resulting sintered roduct.

In testimony whereof I a x my signature.

LLOYD E. TETER. a 

